At the start Legion, for me, Destro definitely bloomed much earlier than the other two specs and had less ramp up. So yes Demo and Affy are both more arty level and gear dependent. However, that also means both scale much better in the long run. Like someone has already said having the correct legendary is not really a thing as Affy is pretty versatile however, that item level boost should help a lot.
Ultimately I would still suggest Affy for levelling as you can dot on the move but all specs work so choose your favourite/what suits your playstyle.